The present invention relates to a power transmission apparatus for a four-wheel drive vehicle, which distributes a driving force output from a transmission coupled to a transverse layout front engine to front and rear wheels.
There is known a four-wheel drive vehicle in which a distribution of a driving force to the rear wheels is controlled by an electromagnetic clutch. In the four-wheel drive vehicle of a type in which the engine is transversely laid out, it is a common practice that the electromagnetic clutch is disposed on a rear drive pinion shaft located in the rear part of the vehicle body, as disclosed in a Japanese Utility Model Unexamined Publication No. Hei. 7-14229.
In the case where the electromagnetic clutch is disposed in the rear part of the vehicle body, there is the possibility of increasing the size of harness components, and hence making the structure complicated. The electromagnetic clutch control unit is preferably disposed while being coupled to or in proximity to the engine control unit, the transmission control unit and the like in the vicinity of the engine, transmission and the like (in the front part of the vehicle body). In a case where the electromagnetic clutch control unit is disposed in the front part of the vehicle body, long harness components are required for connecting the electromagnetic clutch to the control unit. This leads to complexity of the structure for protecting the harness components.
The electromagnetic clutch may be disposed in the front part of the vehicle body by disposing the electromagnetic clutch on the axis of the drive shaft of the front wheels or the axis of the pinion shaft of the direction-changing gear.
Where the electromagnetic clutch is disposed on the axis of the front wheel drive shaft, the differential device must be installed at limited places within the transfer. In some types of schematic structure of the vehicle body, the transfer is enlarged in the axle direction, and hence, sometimes the on-board property is deteriorated.
Where the electromagnetic clutch is disposed on the axis of the pinion shaft of the direction-changing gear, the transfer is enlarged to the front and rear directions. In such a case, the electromagnetic clutch of a large diameter overlaps with the steering gear box, a vehicle body schematic structure (cross member and others) and the like above or below those components. If the position of the steering gear box is shifted to another or the cross member is bent in order to secure a good positional relationship of those components with the electromagnetic clutch, there is a chance that the vehicle body structure is complicated, and the number of vehicle models is increased, and other disadvantages occur. The fact that the electromagnetic clutch of the large diameter overlaps with the steering gear box, the cross member and the like above or below those components, sometimes results in reduction of the cabin space and the minimum ground clearance.
Accordingly, an object of the present invention is to provide a power transmission apparatus for use with a four-wheel drive vehicle, which is compact in construction, and excellent in on-board property.
To achieve the above object, there is provided a power transmission apparatus for a four-wheel drive vehicle, according to the present invention comprising:
a transfer disposed on a rear side of a transverse layout front engine, through which a driving force output from a transmission coupled with the transverse layout front engine is distributed to front and rear wheels, the transfer comprising:
a pair of direction-changing gears for changing a transmission direction of the driving force;
a first gear provided and rotated about an axis extending in a transmission direction that has been changed by the direction-changing gears;
a second gear meshed with the first gear and rotated around an axis in parallel with the transmission direction that has been changed by the direction-changing gears, the second gear having a through hole at a center thereof;
an output shaft, rotatably inserted through the through hole of the second gear, for transmitting the driving force to a propeller shaft; and
an electromagnetic clutch disposed on the axis of the second gear and at a position closer to the engine than the second gear and on the center axis of the second gear, the electromagnetic clutch operable to control a transmission torque of the driving force between of a gear shaft portion of the second gear and the output shaft.
In the power transmission apparatus for use with a four-wheel drive vehicle, an electromagnetic clutch container for containing the electromagnetic clutch may be independently provided within a transfer case of the transfer, and the electromagnetic clutch container is liquid-tightly separated from another container for containing another member in a manner that oil seals are brought into sliding contact with the outer periphery of the gear shaft portion that is extended into the electromagnetic clutch container.
In addition, the above-mentioned object can also be achieved by a power transmission apparatus for a four-wheel drive vehicle, according to the present invention, comprising:
a transfer disposed on a rear side of a transverse layout front engine, through which a driving force output from a transmission coupled with the transverse layout front engine is distributed to front and rear wheels, the transfer comprising:
a pair of direction-changing gears for changing from a first transmission direction of the driving force to a second transmission direction of the driving force;
a first gear provided and rotated about an axis extending in the second transmission direction;
a second gear meshed with the first gear and rotated around an axis in parallel with the second transmission direction, the second gear having a through hole at a center thereof;
an output shaft, rotatably inserted through the through hole of the second gear, for transmitting the driving force to a propeller shaft; and
an electromagnetic clutch disposed on the axis of the second gear and between the transverse layout front engine than the second gear, the electromagnetic clutch operable to control a transmission torque of the driving force between the second gear and the output shaft.
In an embodiment of the power transmission apparatus, according to the present invention, may further comprise:
a transfer case containing the transfer;
an electromagnetic clutch container containing said electromagnetic clutch, said electromagnetic clutch container being independently provided within the transfer case; and
a seal member liquid-tightly sealing said electromagnetic clutch container, said seal member being brought into sliding contact with an outer periphery of a a gear shaft portion of said second gear that is extended into said electromagnetic clutch container.